# Document an Elixir Module with a README in 2026 using Atlas

> Atlas helps Elixir developers generate accurate README documentation by reading source code and verifying examples with `ExUnit via mix test`.

Atlas, the terminal-native AI coding agent, empowers Elixir developers in 2026 to produce precise documentation for modules by directly reading source code and verifying examples. It integrates direct with the Elixir toolchain, utilizing `Mix and Hex` for dependency management, `ExUnit via mix test` for verification, and `mix format` for code consistency, ensuring your READMEs reflect the current state of your codebase, not outdated assumptions.

## Key takeaways

- Atlas generates Elixir module READMEs directly from source code, ensuring accuracy and traceability.
- It leverages `lsp` to enumerate public APIs and `codebase_search` for real-world Elixir usage examples.
- Atlas uses `grep` to match existing `README.md` styles, maintaining consistency across your `mix` project.
- Every code sample in the generated Elixir documentation is verified by `bash` execution, preventing outdated examples.
- Atlas provides a unified diff for all proposed changes, requiring explicit approval before writing to your Elixir codebase.
- Integration with `git` allows Atlas to manage commits and provide rollback capabilities for Elixir documentation updates.

## How Atlas Generates Accurate Elixir Module Documentation

Atlas generates accurate Elixir module documentation by directly inspecting your project's source code, ensuring every claim traces back to a real file. In 2026, this process begins by enumerating the public API of an Elixir module using the `lsp` tool's `documentSymbol` operation, preventing any exports from being missed or invented.

To create a README that truly reflects an Elixir module's current behavior, Atlas first uses its `lsp` tool to identify all public functions and macros within a module, such as `lib/my_app/my_module.ex`. This ensures that the documentation covers the module's entire exported surface. Following this, Atlas employs its `read` tool to understand the implementation details of each export. To provide practical context, the `codebase_search` tool then scans the Elixir project to find real-world usage examples, showing how other parts of your OTP application or `mix` project interact with the module. This hybrid semantic and keyword retrieval, fused by reciprocal rank fusion, ensures a comprehensive understanding of the module's role and actual usage patterns, moving beyond theoretical descriptions to concrete, verifiable behavior.

## Ensuring Consistency and Verifying Code Samples in Elixir READMEs

Atlas ensures consistency in Elixir READMEs by first searching for existing documentation patterns within your `mix` project. The `grep` tool is used to locate an existing `README.md` file, allowing Atlas to match its heading structure and tone rather than inventing a new format in 2026.

After gathering information about the module's API and usage, Atlas uses its `grep` tool to find any existing `README.md` files in your Elixir project. This step is crucial for maintaining a consistent documentation style across your codebase, whether it's a single `mix` project or a larger OTP application. Once the README content is drafted using the `write` tool, quoting real Elixir function signatures and file paths like `lib/my_app/my_module.ex`, Atlas takes a critical step: verifying every code sample. The `bash` tool executes these samples, ensuring they run correctly and produce the expected output. A code sample that has never been executed is a liability, and Atlas's verification process, which can include running `mix test` for specific examples, guarantees that your documentation remains a reliable source of truth for Elixir developers.

## Atlas's Safety and Review Mechanisms for Elixir Documentation Edits

Atlas incorporates robust safety and review mechanisms for all Elixir documentation edits, ensuring developers maintain full control over changes in 2026. Every Atlas tool call, including `lsp`, `read`, `grep`, `write`, and `bash`, is permission-gated against allow, ask, and deny rules before execution.

Before any changes are applied to your Elixir project's `README.md` or source files, Atlas drafts a plan in a read-only plan agent and explicitly asks for your approval. This transparent approach extends to the build agent, where Atlas computes a unified diff for every proposed file edit. This diff is then surfaced for your approval, allowing you to review precisely what will be written to your `README.md` or `lib/my_app/my_module.ex` files. Atlas also reads `git` branches, status, and diffs, and can stage and create commits on your behalf, providing a complete version control integration. Furthermore, Atlas snapshots file changes as `git` patches, enabling easy diffing and rolling back of edits, ensuring that documentation updates are both accurate and reversible within your Elixir development workflow.

## Integrating Atlas with Your Elixir Development Environment

Integrating Atlas into your Elixir development environment is straightforward, allowing you to leverage its capabilities within your existing `mix` projects and OTP applications. In 2026, you simply run `atlas` in a project containing a `mix.exs` file, and it begins indexing your code.

Atlas builds its code index using AST declarations via tree-sitter, not blind line windows, providing a deep understanding of your Elixir codebase's structure, including supervision trees, contexts, and dependencies managed by `Mix and Hex`. You can configure Atlas to build its code index with local Ollama embeddings, keeping your proprietary Elixir code off third-party servers. Atlas is a terminal-native TUI rendered with SolidJS through the OpenTUI renderer, offering a responsive and customizable experience with a charcoal-and-blue default theme and many presets. You can switch the active model and provider on the fly with favorites and recents, and extend Atlas through plugins that contribute tools and hook into agent lifecycle events, making it a flexible partner for Elixir developers.

## Steps

1. Initialize Atlas in your Elixir project by navigating to your project root (containing `mix.exs`) and running `atlas`.
2. Instruct Atlas to enumerate the public API of your target Elixir module (e.g., `lib/my_app/my_module.ex`) using the `lsp` tool's `documentSymbol` operation.
3. Ask Atlas to `read` the implementation of each public function and use `codebase_search` to find practical usage examples across your `mix` project.
4. Direct Atlas to `grep` your repository for an existing `README.md` to match its structure and tone for the new module documentation.
5. Command Atlas to `write` the new `README.md` for your Elixir module, ensuring it quotes real function signatures and file paths.
6. Review the proposed `README.md` changes presented as a unified diff by Atlas, approving or modifying as needed.
7. Instruct Atlas to `bash` execute all code samples within the drafted `README.md` to verify their correctness, potentially involving `ExUnit via mix test` for specific examples.
8. Approve the final `README.md` and allow Atlas to stage and commit the changes to your Elixir project's `git` repository.

## FAQ

### How does Atlas ensure Elixir documentation is always up-to-date?

Atlas ensures Elixir documentation is current by reading the live source code with its `read` tool and verifying code samples with `bash`. It doesn't rely on outdated assumptions, but on what the code in `lib/my_app/my_module.ex` actually does today.

### Can Atlas integrate with my existing Elixir `mix` project structure?

Yes, Atlas is designed for Elixir `mix` projects and OTP applications. It reads your `mix.exs` file, understands supervision trees and contexts, and indexes code by AST declarations using tree-sitter for deep structural awareness.

### What Elixir tools does Atlas use for verification?

Atlas uses the `bash` tool to execute code samples directly from the documentation. For Elixir, this can include running specific `ExUnit via mix test` commands to validate examples and ensure they function as described.

### How does Atlas handle sensitive Elixir code when generating documentation?

Atlas can build its code index with local Ollama embeddings, keeping your Elixir code off third-party servers. Additionally, every Atlas tool call is permission-gated, requiring your explicit approval before accessing or modifying files like `lib/my_app/my_module.ex`.

### Can I review and approve changes before Atlas writes them to my Elixir `README.md`?

Absolutely. Atlas operates with a read-only plan agent and presents a unified diff for every proposed file edit. You must explicitly approve these changes before Atlas uses its `write` tool to modify your Elixir project's `README.md`.

### Does Atlas support Elixir's `mix format` for code style?

While Atlas's primary role is documentation generation and verification, it respects your Elixir project's existing toolchain. It can be configured to ensure generated code samples adhere to `mix format` standards, maintaining consistency.

### How does Atlas find relevant Elixir code usage examples?

Atlas uses its `codebase_search` tool, which employs hybrid semantic and keyword retrieval fused by reciprocal rank fusion, to find how callers actually use your Elixir module's exports in practice across your `mix` project.

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Canonical HTML: https://runatlas.sh/resources/stacks/document-a-module-with-a-readme-in-elixir
Source of truth: aeo_pages row `/resources/stacks/document-a-module-with-a-readme-in-elixir` (segment: Stacks) (this file is generated from it, never hand-edited).
Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.